Checkout submodules

.github/workflows/cmake.yml

@@ -16,6 +16,9 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
+    
+    - name: Checkout submodules
+      run: git submodule init
 
     - name: Create Build Environment
       # Some projects don't allow in-source building, so create a separate build directory